Author Topic: Taking multi-hour temperature slices before tire pressure measurement  (Read 338 times)

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Offline DesertBlue

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Hi all -- I want to get detailed correlation data on ambient temperature and vehicle tire pressure under different conditions (including nitrogen-filled tires). It occurred to me that temperature at the moment of tire pressure measurement might not be the best predictor. If the temperature has changed over time leading up to that point, then maybe where it was 30 minutes ago is more relevant to tire pressure than where it is right now.

Does anyone know what the lag is expected to be for effects on gas pressure in this context? How would you construct a temperature variable if you wanted to account for change? The simplest would be to average T1 and T2 or something, playing with the time interval, or plug in a lot more points.

By the way, I assumed that temperature sensors are real-time, or instantaneous in their readings, with no lag behind changes. But is this true? Is there more than a couple of seconds of lag in reflecting the true ambient temperature? I assume that temperature changes don't have to "travel" through any significant material insulating a sensor.

Thanks.

Offline SteveFitz1

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Re: Taking multi-hour temperature slices before tire pressure measurement
« Reply #1 on: October 10, 2021, 12:18:22 PM »
Try searching "temperature vs air pressure". You'll find lots of articles that will probably answer your question. Here's an interesting one, for example: https://billanddot.com/tire-pressure-vs-temp-calc.html

Offline vreihen

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Re: Taking multi-hour temperature slices before tire pressure measurement
« Reply #2 on: October 10, 2021, 02:06:18 PM »
Some automotive TPMS system sensors also report temperature, even if the vehicle does not display it for the driver's viewing.

If the TPMS sensors in your car report temperature and are readable by rtl_433, it could be interesting to drive around with a Raspberry Pi and USB SDR receiver to plot the pressure rise as the tires warm up.

FYI, the main reason why motorsports folks use nitrogen in their tires is to avoid the water vapor that always winds up in the air from a compressor...even with driers in the line.  Nitrogen supposedly has less expansion than wet air when the temperature rises, making the expansion curve more predictable when setting pressures in a critical application.....
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Offline DesertBlue

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Re: Taking multi-hour temperature slices before tire pressure measurement
« Reply #3 on: October 12, 2021, 12:56:29 PM »
Try searching "temperature vs air pressure". You'll find lots of articles that will probably answer your question. Here's an interesting one, for example: https://billanddot.com/tire-pressure-vs-temp-calc.html

Thanks, that's a very interesting tool.

Offline DesertBlue

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Re: Taking multi-hour temperature slices before tire pressure measurement
« Reply #4 on: October 12, 2021, 01:01:08 PM »
Some automotive TPMS system sensors also report temperature, even if the vehicle does not display it for the driver's viewing.

If the TPMS sensors in your car report temperature and are readable by rtl_433, it could be interesting to drive around with a Raspberry Pi and USB SDR receiver to plot the pressure rise as the tires warm up.

FYI, the main reason why motorsports folks use nitrogen in their tires is to avoid the water vapor that always winds up in the air from a compressor...even with driers in the line.  Nitrogen supposedly has less expansion than wet air when the temperature rises, making the expansion curve more predictable when setting pressures in a critical application.....

I didn't know about the motorsports angle. The reason people use it on regular cars is that the tires lose "air" more slowly than if they use normal air, so tire pressure is more stable and requires less frequent adjustment. It's a minor benefit, especially since any eventual adjustment in terms of adding "air" is impossible at home anyway since people won't have nitrogen tanks or whatever, and would need to go back to the tire shop. But at some places nitrogen fill is free or included with any tire purchase, like at Costco's tire shops.

 

anything